This application is copending with application No. 8/024,967, filed Mar. 2, 1993, now U.S. Pat. No. 5,368,836.
The invention relates to the clathrasil of the dodecasil 1 H structural type having a small average particle size, to platelet-like pigments based on such particles and to the corresponding preparation processes.
Clathrasils belong to the class of porous tectosilicates or porosils, which, according to H. Gies and B. Marler, Zeolites, 12 (1992), 42, can be described by the general formula ##EQU1## in which A is a cation of charge y, T is a trivalent cation which is coordinated tetrahedrally by 4 oxygen atoms, z is the number of additional oxygen atoms for compensating for lattice interruptions, AX are ion pairs and M are guest particles and u, v and w are 0, 1, 2. Examples of suitable cations A are alkali metal ions or alkaline earth metal ions, T can be, for example, an aluminum cation or a boron cation, and, as X, a large number of anions, such as, for example, OH, halogen, and the like are suitable. The alkali metal and alkaline earth metal ions serve for the charge compensation of the aluminum and boron cations. Na is a preferred alkali metal ion and Ca is a preferred alkaline earth metal ion. The guest particles, which are also designated as templates, are incorporated in the interstices of the porosil structure of the porosils during their synthesis. The guest particles are in general neutral molecules, although, in particular in the case of charges porosil structures, other charges guest particles can sometimes also be incorporated, i.e., to ##EQU2## in which W is the number of charged guest molecules and Q is the number of charges. In this case, the above formula (1) has to be modified accordingly.
Depending on the size and form of the interstices, porosils are divided into clathrasils and zeosils. While zeosils have cage- or channel-like pores which are large enough for the template molecules to be driven off from the pores under relatively mild conditions and, if desired, exchanged for other guest molecules, clathrasils have very small cage-like interstices whose openings are too small for any trapped molecule to leave the pore system. Clathrasils of the dodecasil 1 H type, which have a platelet-like, hexagonal structure, are of particular interest.
Hitherto, clathrasils have been prepared by hydrothermal crystallization at, for example, 200.degree. C. from a silicate-containing solution to which template molecules, such as, for example, adamantylamine have been added. However, in this preparation process, crystals having an average size of typically 150-500 .mu.m are formed. However, crystals of such a large size are not suitable for incorporation in paint formulations, coatings, and the like, and are moreover highly sensitive to cracking. Moreover, the template molecules used in excess in the customary synthesis processes are usually those whose dimensions correspond as closely as possible to the dimensions of the interstices in the dodecasil 1 H; examples which may be mentioned are: 1-adamantylamine, piperidine or azabicyclononanium iodide. However, the materials mentioned are relatively expensive and unsuitable for economical pigment preparation on an industrial scale.
Accordingly, there was a need for clathrasils of the dodecasil 1 H structural type having a small average crystal size of less than about 20 .mu.m and for a corresponding economical preparation process which is suitable for industrial scale production.